The present invention relates to a magnetic head that reads magnetically recorded data, the process of fabricating the magnetic head, and magnetic disc storage apparatus mounting the magnetic head and in particular to a magnetic head having a high S/N ratio and a high yield and a magnetic disc storage apparatus mounting the magnetic head.
A magneto-resistive sensor using a magnetoresistance effect, which causes electrical resistance to vary with a change in an external magnetic field, is known to be an excellent magnetic field sensor and therefore, it has been put into practical use as a read sensor for detecting a signal magnetic field from a magnetic recording medium storage in the magnetic head, an important part of the magnetic disc storage apparatus.
Recording density of the magnetic disc storage apparatus has remarkably improved and is now continuously improving and the need for the read sensor with two improved characteristics has arisen, namely a smaller track width and a higher recording/read performance. At present, the read characteristic is being supersensitized by evolving an MR head using the magnetoresistance effect. At several Gb/in2 of recording density, an anisotropic magnetoresistance (AMR) effect is used to convert magnetic signals on the magnetic recording medium into electric signals and at a higher recording density, a supersensitive giant magnetoresistance (GMR) effect is employed.
To meet the need for the higher recording density, research and development of a method, in which a detect current flows in an almost perpendicular to the plane of the film, have been conducted. This method which is called the CPP (Current Perpendicular to the Plane) method has an advantage in narrowing a distance between the upper and lower shield layers (read gap length). The read sensors using a CPP-GMR or tunneling magnetoresistance (TMR) effect have already been reported.
FIGS. 1 and 2 show a basic structure of a CPP read sensor. FIG. 1 shows the cross section along track width direction of a CPP type read sensor. X, Y and Z axes shown in FIG. 1 indicate the track width direction, sensor height direction, and thickness direction of the magnetoresistance layer, respectively. It should be noted that the X, Y, and Z axes in all the drawings in this specification indicate the same X, Y, and Z axes shown in FIG. 1. The refill film 1 along the track width direction is disposed in contact with the surface of the side wall of a magnetoresistance layer 3. A longitudinal bias layer or a side shield layer 5 is not always necessary. In FIGS. 1, 2 and 4 indicate the upper shield layer and the lower shield layer, respectively.
FIG. 2 is a cross sectional diagram along the CPP sensor height direction taken along an aa′ line shown in FIG. 1. In FIG. 2, on a right side, an air bearing surface 13 of the read sensor is shown. Like the refill film along the track width direction, the refill film along the sensor height direction 6 is disposed in contact with the wall surface of the magnetoresistance layer. The refill film 1 along the track width direction and the refill film along the sensor height direction 6 are made of the insulator such as alumina.
As shown in FIG. 2, the present invention relates to the magnetic head having at least an under layer 51, a pinned layer 52, an intermediate layer 53, a free layer 54, and a cap layer 55, all of which are composing elements of the magnetoresistance layer 3. In the accompanying drawings of the specification, the pinned layer 52 is disposed at a position closer to the lower shield layer 4 than to the free layer 54; nevertheless, the positions, at which the pinned layer 52 and the free layer 54 are disposed, may be switched. The under layer 51 and the cap layer 55 may include such layers that provide functions of controlling a magnetic domain and of stabilizing the magnetization orientation of the pinned layer 52 or the like, respectively. In FIG. 1 and FIGS. 3 and 4 described later, in particular, the detailed structure of the magnetoresistance layer 3 is omitted; however, it should be noted that the magnetoresistance layer 3 has the same structure as that shown in FIG. 2.
In the CPP read sensor, the upper shield layer 2 and the lower shield layer 4 come usually in electrically contact with the magnetoresistance layer 3 to minimize its read gap length. In other words, the upper shield layer 2 and the lower shield layer 4 have the function as the electrode for flowing a current into the magnetoresistance layer 3.
FIG. 3 is a flow diagram showing a process of forming the sensor height. In a process of patterning the magnetoresistance layer to form the sensor height, the magnetoresistance layer 3 is protected with the lift-off mask 11 as shown in FIG. 3(a), and then unnecessary regions are etched away as shown in FIG. 3(b). In this etching process, an ion beam etching method using Ar ions or a Reactive Ion Etch (RIE) method using a chlorine gas or carbon dioxide gas is used generally. After etching, the refill film along the sensor height direction 6 is formed as shown in FIG. 3(c). And then, the lift-off mask 11 and unnecessary portions of the refill film are removed as shown in FIG. 3(d) to form the sensor height of the magnetoresistance layer 3. Subsequently, as shown in FIG. 3(e), the upper shield layer 2, which also acts as an upper electrode, is deposited on the magnetoresistance layer 3 and the refill film along the sensor height direction 6.
To meet the need for increasing the recording density, the track width has been narrowed to 100 nm now. It is required that the sensor height has the same size as the track width to minimize an effect of shape magnetic anisotropy on the free layer.
A patent document JP-A No.085711/2003 discloses a structure, in which the refill film has been disposed on the upper part of a magnetoresistance layer to cause a sense current to flow only in the vicinity of an air bearing surface of a magnetoresistance layer. This technique allows the sense current to concentrate only in the vicinity of the air bearing surface of the magnetoresistance layer; however, it has a disadvantage in that any ingenuity, such as the use of multi layer resist, is necessary and it is difficult to control the length of the refill film on the upper part of a magnetoresistance layer.
To fabricate a smaller sensor height, a process of forming the sensor height without fence or lift-off error is necessary. It is because if fence or lift-off error occurs, the magnetoresistance layer may have loose contact with the upper shield layer. The patent document JP-A No. 186673/2004 discloses a method for using the Chemical Mechanical Polishing (CMP) method in the lift-off process to remove the resist patterns and fence, avoiding lift-off error (incomplete removal of the lift-off mask material) and fence.
A process of lift-off using CMP may damage the upper surfaces of the magnetoresistance layer and of the refill film when the resist patterns and fence are removed. The patent document JP-A No. 186673/2004 discloses a method, by which a first stopper layer and a second stopper layer are deposited on the magnetoresistance layer and the refill film respectively, to avoid any damage to the upper surfaces of the magnetoresistance layer and of the refill film. These stopper layers are made of Diamond-Like Carbon (DLC).
FIG. 4 is a schematic diagram of a process of lift-off using CMP. As shown in FIG. 4(a), first, the first stopper layer 41 and then the lift-off mask 11 are deposited on the magnetoresistance layer 3. As shown in FIG. 4(b), second, the first stopper layer 41 is etched and then, as shown in FIG. 4(c), the magnetoresistance layer 3 is patterned by etching. As shown in FIG. 4(d), third, the refill film along the sensor height direction 6 and the second stopper layer 42 are deposited and then as shown in FIG. 4(e), unnecessary portions of the lift-off mask 11 and the refill film along the sensor height direction 6 are lifted off by CMP. As shown in FIG. 4(f), finally, the first stopper layer 41 and the second stopper layer 42 are removed. The process of lift-off using CMP may solve problems of fence occurrence and lift-off error, which may arise in a conventional lift-off method.
Primary importance is attached to the prevention of the sense current from leaking, and various leakage prevention ideas are tried to meet the need for increasing recording density. The patent document JP-A No.241763/2004 discloses a method, by which after etching, the wall surface of the magnetoresistance layer is oxidized to prevent the sense current from leaking and sensor characteristics from deteriorating in an annealing process. The patent document JP-A No.060266/2003 discloses a method for preventing the magnetoresistance layer from being damaged during air bearing surface processing and the sense current from leaking by wet-etching polishing.